cortical bone

(redirected from Compact tissue)

bone

[bōn]

1. the hard, rigid form of connective tissue constituting most of the skeleton of vertebrates, composed chiefly of calcium salts.

2. any distinct piece of the skeleton of the body. See anatomic Table of Bones in the Appendices for regional and alphabetical listings of bones, and see color plates 1 and 2. Called also os. adj., adj bo´ny.

There are 206 separate bones in the human body. Collectively they form the skeletal system, a structure bound together by ligaments at the joints and set in motion by the muscles, which are secured to the bones by means of tendons. Bones, ligaments, muscles, and tendons are the tissues of the body responsible for supporting and moving the body.

Some bones have a chiefly protective function. An example is the skull, which encloses the brain, the back of the eyeball, and the inner ear. Some, such as the pelvis, are mainly supporting structures. Other bones, such as the jaw and the bones of the fingers, are concerned chiefly with movement. The bone marrow in the center manufactures blood cells. The bones themselves act as a storehouse of calcium, which must be maintained at a certain level in the blood for the body's normal chemical functioning.

Structure and Composition. Bone is not uniform in structure but is composed of several layers of different materials. The outermost layer, the periosteum, is a thin, tough membrane of fibrous tissue. It gives support to the tendons that secure the muscle to the bone and also serves as a protective sheath. This membrane encloses all bones completely except at the joints where there is a layer of cartilage. Beneath the periosteum lie the dense, hard layers of bone tissue called compact bone. Its composition is fibrous rather than solid and it gives bone its resiliency. Encased within these layers is the tissue that makes up most of the volume of bone, called cancellous or spongy bone because it contains little hollows like those of a sponge. The innermost portion of the bone is a hollow cavity containing marrow. Blood vessels course through every layer of bone, carrying nutritive elements, oxygen, and other products. Bone tissue also contains a large number of nerves. The basic chemical in bone, which gives bone its hardness and strength, is calcium phosphate.

Development. Cartilage forms the major part of bone in the very young; this accounts for the great flexibility and resiliency of the infant skeleton. Gradually, calcium phosphate collects in the cartilage, and it becomes harder and more brittle. Some of the cartilage cells break loose, so that channels develop in the bone shaft. Blood vessels enter the channels, bearing with them small cells of connective tissue, some of which become osteoblasts, cells that form true bone. The osteoblasts enter the hardened cartilage, forming layers of hard, firm bone. Other cells, called osteoclasts, work to tear down old or excess bone structure, allowing the osteoblasts to rebuild with new bone. This renewal continues throughout life, although it slows down with age.

Cartilage formation and the subsequent replacement of cartilage by hard material is the mechanism by which bones grow in size. During the period of bone growth, cartilage grows over the hardened portion of bone. In time, this layer of cartilage hardens as calcium phosphate is added, and a fresh layer grows over it, and it too hardens. The process continues until the body reaches full growth. Long bones grow in length because of special cross-sectional layers of cartilage located near the flared ends of the bone. These harden and new cartilage is produced by the same process as previously described.

Bone Disorders. fracture, a break in the bone, is the most common injury to the bone; it may be closed, with no break in the skin, or open, with penetration of the skin and exposure of portions of the broken bone. osteoporosis is excessive brittleness and porosity of bone in the aged. osteomyelitis is a bone infection similar to a boil on the skin, but much more serious because blood supply to bone is less exquisite than that to other body organs and bone metabolizes more slowly, so that the infection can destroy the bone and invade other body tissues. osteomalacia is the term used for rickets when it occurs in adults. In these diseases there is softening of the bones, due to inadequate concentration of calcium or phosphorus in the body. The usual cause is deficiency of vitamin D, which is required for utilization of calcium and phosphorus by the body. In osteitis fibrosa cystica, bone is replaced by fibrous tissue because of abnormal calcium metabolism. The condition usually is due to overactivity of the parathyroid glands. osteoma refers to abnormal new growth, either benign or malignant, of the tissue of the bones. Although it is not common, it may occur in any of the bones of the body, and at any age.

alveolar bone the thin layer of bone making up the bony processes of the maxilla and mandible, surrounding and containing the teeth; it is pierced by many small blood vessels, lymphatic vessels, and nerves.

cortical bone the compact bone of the shaft of a bone that surrounds the marrow cavity.

cranial b's the bones that constitute the cranium, including the occipital, sphenoid, temporal, parietal, frontal, ethmoid, lacrimal, and nasal bones, the inferior nasal concha, and the vomer. Some authorities also include the maxilla, zygomatic bone, and palatine bone. See anatomic Table of Bones in the Appendices.

ethmoid bone the sievelike bone that forms a roof for the nasal fossae and part of the floor of the anterior cranial fossa. See anatomic Table of Bones in the Appendices.

facial b's the bones that form the skeleton of the face, including the hyoid, palatine, and zygomatic bones, the mandible, and the maxilla. Some authorities include the lacrimal bones, nasal bones, inferior nasal concha, and vomer and exclude the hyoid bone. See anatomic Table of Bones in the Appendices.

flat bone one whose thickness is slight, sometimes consisting of only a thin layer of compact bone, or of two layers with intervening cancellous bone and marrow; usually curved rather than flat.

frontal bone the bone at the anterior part of the skull. See anatomic Table of Bones in the Appendices.

hip bone the ilium, ischium, and pubis as a unit. See anatomic Table of Bones in the Appendices.

hyoid bone a horseshoe-shaped bone at the base of the tongue. See anatomic Table of Bones in the Appendices. Called also lingual bone.

incisive bone the portion of the maxilla bearing the incisors; developmentally, it is the premaxilla, which in humans later fuses with the maxilla, but in most other vertebrates persists as a separate bone.

cortical bone

cor·ti·cal bone

cor·ti·cal bone

(kōr'ti-kăl bōn) [TA]

Superficial thin layer of compact bone.

bone

1. the hard, rigid form of connective tissue constituting most of the skeleton of most vertebrates, composed chiefly of an organic component of collagenous matrix and cells and a mineral component of calcium phosphate and other salts.

2. any distinct piece of the skeleton of the body. For a named list of bones see Table 10.

3. describes conformation, substance, thickness and quality of bone structure in an animal, e.g. an animal with good bone. See also osseous.

bone ash

analysis of the degree of mineralization of bone is done by an ash analysis in which the bone is heated at 600°C until there is no further weight loss.

has histological characteristics of both cartilage and bone; may develop in response to tensions from frequently changing directions.

bone clamp

strongly built, handheld, tong-like instrument with outcurving blades making a circle when closed for grasping a piece of bone shaft. The handles are ratcheted to give a firm grasp, and the faces of the blades have deep, crossways grooves.

compact bone

bone substance that is dense and noncancellous.

cortical bone

the compact bone of the shaft of a bone that surrounds the marrow cavity.

bone cyst

a discrete, grossly visible cavity, filled with fluid and often lined by a membrane. It may be located under cartilage (subchondral), be a single cavity (unicameral), filled with blood (aneurysmal) or contain epidermal cells (epidermoid).

one whose thickness is slight, sometimes consisting of only a thin layer of compact bone, or of two layers with intervening cancellated bone and marrow; usually curved rather than flat.

bone flour

finely ground bone used as a mineral supplement in animal feed to supply additional calcium and phosphorus. Needs to be properly sterilized.

bone fragility

the ease with which bone fractures depends to a large extent on the density of its compact bone, that is its degree of mineralization, which in turn depends on a number of factors including age, nutritional adequacy, state of pregnancy and lactation and exposure to weight bearing.

mature bone in which the collagen fibers are in an orderly layered arrangement producing lamellae.

laminar bone

the formation of bone by the periosteum in layers, sometimes more than one layer at a time, to supplement the diaphyseal expansion of the bone. Is marked in farm animals and large dogs, and serves to accommodate the skeleton to the very rapid growth of the musculature.

the intercellular component of bone. It includes collagen and amorphous ground substance consisting mostly of mucopolysaccharides (chondroitin sulfate).

bone meal

a product made from meatless bones which are crushed and sterilized. The bones are derived from boning plants and retail outlets. The bonemeal is used as stock feed, fertilizer and in a number of industries. Care is needed in its preparation and in the selection of the bones because of the high risk of transmitting diseases including anthrax, salmonellosis, tuberculosis. A coarse grade of bone flour (see above). Prohibited from being used as a feed in many countries as part of programs to control or prevent bovine spongiform encephalopathy.

membrane bone

bone that develops within a connective tissue membrane.

metaplastic bone

bone formed by connective tissue by redifferentiation of mesenchymal cells.

bone mineral

principally calcium and phosphorus but includes also magnesium and, to a lesser extent, potassium and fluorine. Consisting mainly of hydrated calcium phosphate (apatite) and calcium carbonate.

bone modeling

the sum of the activities of the endosteum and periosteum of bone to produce bone forms.

low density bone around the lacunae of bone which contains much amorphous mineral. In this form the mineral is labile and therefore important in the maintenance of calcium homeostasis.

periosteal bone

bone deposition by the periosteum in successive laminae; the bone formation in new bone and in a callus, beginning as fibrocellular tissue forming from the endosteum and periosteum, followed by calcification and bone formation.

By measuring the thickness of the compact tissue and external and internal general plates and the number of osteons and their measurements, we have identified certain age morphological differences in bone tissue histoarchitectonics.

The compact tissue close to medullary cavity is smoother compared with the previous age.

One of the structures of guineafowl's long-bone compact tissue is mixed histoarchitectonics, which is observed in the humerus bone (in the lateral, dorsal, and volar sectors of the bone's proximal part; in the diaphysis of the volar and dorsal sector and from the middle of the superficial edge to the middle of the compact tissue of the medial sector; in the bone's distal part of the lateral sector and in the dorsal sector at the perimedullary edge).

During the period of 270-365 days of age, histoarchitectonics of the bone's compact tissue continues to redevelop, but earlier developed basic-support structures stay yet.

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